Obj-Exporter test: fix test fixure if no export was requetsed.

test/unit/utObjImportExport.cpp

@@ -234,6 +234,8 @@ TEST_F( utObjImportExport, issue1111_no_mat_name_Test ) {
     EXPECT_NE( nullptr, scene );
 }
 
+#ifndef ASSIMP_BUILD_NO_EXPORT
+
 TEST_F( utObjImportExport, issue809_vertex_color_Test ) {
     ::Assimp::Importer importer;
     const aiScene *scene = importer.ReadFile( ASSIMP_TEST_MODELS_DIR "/OBJ/cube_with_vertexcolors.obj", 0 );
@@ -242,3 +244,5 @@ TEST_F( utObjImportExport, issue809_vertex_color_Test ) {
     ::Assimp::Exporter exporter;
     EXPECT_EQ( aiReturn_SUCCESS, exporter.Export( scene, "obj", ASSIMP_TEST_MODELS_DIR "/OBJ/test.obj" ) );
 }
+
+#endif // ASSIMP_BUILD_NO_EXPORT